Aberdeen Landslides and Liquefaction Susceptibility Report Published

The Washington State Geologic Survey announces the publication of Report of Investigations 36. Earthquake-induced landslide and liquefaction susceptibility and initiation potential maps for tsunami inundation zones in Aberdeen, Hoquiam, and Cosmopolis, Grays Harbor County, Washington, for a M9+ Cascadia subduction zone event, by S. L. Slaughter, T. J. Walsh, Anton Ypma, K. M. D. Stanton, Recep Cakir, and T. A. Contreras. This publication is available free online at http://www.dnr.wa.gov/Publications/ger_ri36_aberdeen_liquefaction.zip. Additionally, a limited number have been plotted and will be sold through the Washington Department of Enterprise Services for $38.61.

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This report assesses the earthquake-induced ground failure potential, including soil liquefaction and landslides, for the communities of Aberdeen, Cosmopolis, and Hoquiam in Grays Harbor County, Washington.

The probability of soil liquefaction increases with the duration of shaking, and slopes that are stable under static conditions may fail under large ground accelerations. A Cascadia Subduction Zone (CSZ) earthquake of magnitude (M) 9+ could produce ground accelerations on the Washington coast of as much as 0.40 g (g is the acceleration due to gravity) and shaking durations of as much as several minutes, sufficient to initiate soil liquefaction and shallow landslides. Soil liquefaction can damage transportation networks, such as roads and bridges, and landslides; even very small landslides can render a road impassable to automobiles. These ground failures can complicate or prohibit vehicular evacuation, as well as hamper emergency response and recovery efforts.

The objective of this report is to assist city and emergency management officials in evaluating the suitability of existing evacuation routes and assembly areas for potential susceptibility to ground failure from a M9+ CSZ earthquake. Results of this report could indicate the need to modify current evacuation routes and assembly areas. Understanding which areas are more susceptible to ground failure during a large earthquake can help communities prepare for potentially obstructed transportation networks, toppled buildings, and other secondary seismic hazards.